400GB Hard Disk Drives in RAID 0, RAID 5 and RAID 10 Arrays. Part 2

In our today’s article we are going to talk about the ability of seven different 400GB 3.5” hard disk drives to work in RAID arrays of various types. We will test solutions from Hitachi, Samsung, Seagate and Western Digital.

Some time ago we compared different hard disk drives in terms of their usability in RAID arrays (for details see our first article called 400GB Hard Disk Drives in RAID 0, RAID 5 and RAID 10 Arrays: Performance Analysis). Unfortunately, we have not been able to return to that interesting topic for a while, but now we are ready to renew the series of tests. We will continue from the same storage capacity we stopped at in the last test session, namely 400 gigabytes. In the upcoming reviews we will consider newer HDD models with higher-density platters and higher speeds that have appeared on the market recently.

First we want to tell you about the reasons for such testing and the results of the previous test session.

Apart from pure curiosity, the main reason is to check HDDs out under the specific load of a RAID array. On one hand, the load on each particular HDD within an array is reduced because the HDDs share the same request queue, and sequential requests are likely to go to different disks. On the other hand, the requirements to arrays are higher than to single disks, and the firmware algorithms of look-ahead reading, deferred writing and reordering of requests play a much more important role for them. To make things even more complicated, the RAID controller has some memory of its own and takes part in buffering data and request reordering. And this cooperation between the controller and the HDDs is not always smooth. Long ago a RAID0 array might prove to be hardly any faster than a single disk, not two times as fast, as the user expected.

It is also interesting to see the HDDs work in a RAID5 array which is becoming an ever more popular type of RAID. For the user, RAID5 is a simple way to securing his data and increasing the read speed of the disk subsystem, but for the HDDs this array type is quite difficult because each write request to a RAID5 array translates into two reads and two writes.

We got very interesting results during our previous test session. We could see that NCQ technology really worked and helped improve the performance of a RAID array if supported by the HDDs. This was good indeed because early NCQ-supporting HDDs had behaved rather oddly, often proving to be slower than their NCQ-less predecessors. Another interesting fact was that server-oriented HDDs had no real advantage over their “desktop” counterparts.